In this study, a numerical study is performed on the thermal flow characteristics of a pyrolysis reactor to which an ejector was applied that enables heat recovery through internal gas recirculation. Depending on the ejector figure, the recirculation rate of the high temperature internal gas in the reactor is increased upto a maximum of 6.49 %, and the heat recovery rate is improved upto 14.7 %. In addition, a high-temperature internal gas circulation rate of 3.39 % is observed in a small-scale model based on the similitude theory. Among the silicon dioxide particles introduced into the small-scale reactor, the maximum particle diameter released through the outlet was numerically measured to be 78 ㎛, and about 40 % of the silicon dioxide particles were collected from the internal recirculation path at the bottom of reactor.